I have my 4890 in my W.C loop, with a full cover koolance block.
I have been trying for days to figure out why I could not get the Voltage tweak software to work.

After many different software trials, (different drivers, versions of the program, different OS) I tried going the hardware route. I took apart my stock cooler, took out the fan, and plugged it into my card (with the fullcover block still attached) and left the fan to hang there.

And what do you know, it works. I am able to use the program and increase the voltage on this puppy. The only problem: the fan is still hanging there, and its loud as hell.

I need to figure out a way to "trick" my card into "thinking" that it has a fan plugged in.

Either a software or hardware/mod solution will do. I will not mess with the bios unless it is the only way to fix it.